1. Field of the Invention
This invention relates to a semiconductor chip kit, especially of a type permitting clock signals with a plurality of clock frequencies to be input.
2. Description of the Prior Art
A semiconductor chip kit as shown in FIG. 9 has been used conventionally as one having a plurality of ICs requiring clock signals. The semiconductor chip kit SCK as shown in FIG. 9 has been used as a circuit in a high frequency portion in a portable terminal of a mobile wireless system, for example. PLL-IC (phase-locked loop IC) and IF-IC (intermediate frequency IC) having built-in filters are examples of ICs requiring a clock signal. The semiconductor chip kits SCK of this type are configured to supply a clock signal to individual ICs from a single clock generator. That is, as shown in FIG. 9, a single clock generator 10 supplies a clock signal to individual ICs, i.e., the fist IC 21, second IC 22 and third IC 23. The clock generator 10 used as the clock supply source most typically used in semiconductor chip kits SCK in mobile wireless systems is TCXO (temperature-compensated Xeal oscillator) for a synthesizer.
In the semiconductor chip kit SCK shown in FIG. 9, it was often necessary to change the clock frequency of the clock signal generated by the clock generator 10. Especially in semiconductor chip kits SCK used in mobile wireless systems, the clock frequency of the clock signal generated by the clock generator 10 had to be more often changed for the purpose of avoiding cross modulation with peripheral circuits, commonly using it with a control clock, or permitting peripheral circuits to be made by using general purpose chips. When the clock frequency of the clock signal generated by the clock generator 10 is changed, also the clock frequency of the first IC 21, second IC 22 and third IC 23 heretofore receiving the clock signal from the clock generator 10 had to be changed. That is, all of ICs had to be changed in specification to change the clock frequency. In this case, all ICs had to be redesigned, and a great deal of labor was required therefor.
As shown in FIG. 9, some semiconductor chip kits had clock frequency switches 21a, 22a, 23a provided for the first IC 21, second IC 22 and third IC 23 for switching clock signals to meet different kinds of clock frequencies to a certain extent. That is, such semiconductor chip kits were configured to change over circuits on the part of ICs to cope with different kinds of clock frequencies. In this case, however, clock frequency changeover switches 21a, 22a and 23a were required outside the first IC 21, second IC 22 and third IC 23, respectively, and there arose the need for more IC pins and a bulky scale of IC. In other words, the use of such switches was away from the requirements of reducing IC pins and miniaturization of ICs. Additionally, ICs had to be designed on presumption of possible clock frequencies to switch to. Nevertheless, for clock frequencies other than those the ICs were designed for, all ICs still had to be replaced.
Moreover, since all of the first IC 21, second IC 22 and third IC 23 were supplied with a clock signal from a single clock generator 10, the load to the clock generator 10 was too heavy. Therefore, a buffer device had to be provided to assist the clock generator 10, and it invited an increase in number of parts or elements.